The present invention relates to energy absorbers or shock absorbers and energy transferring connectors and, particularly to energy absorbers and connectors for use in connection with safety systems such as horizontal lifeline systems.
The following information is provided to assist the reader to understand the invention disclosed below and the environment in which it will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the present invention or the background of the present invention. The disclosure of all references cited herein are incorporated by reference.
Energy absorbers or shock absorbers absorb energy to, for example, protect against damage to equipment and/or to protect against injury to person(s). Energy absorbers have, for example, been used in fall protection as part of a fall-arresting safety system such as a horizontal lifeline system. Horizontal lifeline systems include a generally horizontal line connected between supports such as stanchions to which safety lines of individual workers can be connected. See, for example, U.S. Pat. No. 6,722,470.
As part of a requirement established by the United States Occupational Safety and Health Administration (OSHA) and the American National Standards Institute (ANSI) horizontal lifeline systems shall be designed to maintain a factor of safety of at least 2. Because of other regulations, fall protection components (for example, connectors etc.) are typically manufacture to have a rating (for example, an ultimate tensile load) of 5,000 lbs. Therefore, for fall protection manufacturers to use components commonly used with other fall protection systems (which components typically have a rating of 5000 lbs. as described above), it is advantageous to prevent loads in horizontal lifeline systems from exceeding 2,500 lbs (that is, 5,000 lbs with a 2:1 safety factor). To maintain minimal cable extension and suitable overall fall clearance distance below the workers using the horizontal lifeline, it is preferably to maintain loads as close to 2,500 lbs. as possible. Nonetheless, in certain systems, horizontal lifeline stanchions can be subjected to substantial force.
The purpose of an energy or shock absorber in a horizontal lifeline system is to absorb the energy from a fall and thereby limit the forces to below a certain force (for example, the 5000 lbs of force with a 2:1 safety factor). Although there are many types of energy absorbers that perform this function, a design problem common to all such energy absorbers is how to accommodate the force requirements at initial deployment or activation. Regardless of whether an energy absorbers performs consistently and within design and regulatory requirements during the continuous stage following initial deployment, care must be taken during design of the energy absorber to ensure that such requirements are satisfied during the dynamic, initial activation of the energy absorber.
In one type of energy absorber, a strip of metal is connected between two elements so that the metal tears when subjected to force exceeding a certain threshold force across the two elements. U.S. Pat. No. 6,279,680 discloses the use of such an energy absorber in a horizontal lifeline system. Tearing of the metal in this type energy or shock absorber absorbs energy. To ensure that such an energy absorber satisfies design and regulatory requirements during initial activation, it can be necessary for the manufacture to subject the energy absorber to an initial “pre-tear” process in which the energy absorber is subjected to sufficient force to initiate a small degree of tearing.
Several other problems are associated with energy absorbers including a strip or strap of material that is tom. For example, such energy absorbers typically tear such that one section of the strap thereof is pulled to move in a first direction, while a second section of the strap is pulled to move in a second direction, generally opposite of the first direction. Although the strap can, for example, be coiled by the manufacturer so that the energy absorber originally takes up little space, the activation and full (or even partial) deployment (including both uncoiling and tearing) of the energy absorber results in a spent strap that is relatively large in total length/area. Such an energy absorber may not be suitable for uses in which there is limited space for the spent energy absorber or in which it is desirable to limit total displacement.
Although a number of energy absorbers are available for use in connection with fall protection and other systems, it remains desirable to develop improved energy absorbing devices, systems and methods.